Summarize the contents of Jekyll's letter/request written to Lanyon, and what action did Lanyon take in response to it?

Lanyon received a very urgent letter from Jekyll that requested he follow very specific instructions by going to Jekyll's home and retrieving a specific drawer from his cabinet. Poole was to help him get into the upper room. Lanyon was to fetch the drawer and all of its contents and immediately return to his home. A messenger from Jekyll would come to claim the ingredients at midnight. There was no explanation of why Jekyll needed Lanyon to complete these tasks, but there was such a severe sense of urgency that Lanyon felt he should comply.